BREAKING CHANGE: The `render` method on `Renderer`, `HelpRequest`, and `ProgramCollect` now returns `RenderResult` instead of taking `&mut RenderResult`. The `r_print!` and `r_println!` macros have been removed in favor of using `std::io::Write` directly on `RenderResult`.
Add module-level docs for the hook system, enhance doc examples for macros with usage syntax, fix typos in cross-references, and hide internal debugging macros and mock types from public documentation
Extract duplicate `MockCollect` implementations into a reusable `MockProgramCollect` type. Conditionally require `Serialize` on the `Groupped` trait when the `general_renderer` feature is enabled.